Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to deactivatable magnetomechanical markers and labels for electronic article surveillance (EAS) systems, and more particularly to using a mechanical mechanism and a high magnetostrictive material as a deactivatable bias to reduce tag pollution due to magnetomechanical EAS markers.
2. Description of the Related Art
EAS systems are typically used to prevent unauthorized removal of items from a designated area. In a retail environment, EAS labels are attached to articles for sale, and when active, will trigger an alarm if carried through interrogation zones typically located at the store exits. After an authorized sale of an article, store personnel deactivate the attached EAS label so the article can be removed from the store without triggering the EAS system. As used herein, the terms xe2x80x9cmarkersxe2x80x9d, xe2x80x9clabelsxe2x80x9d, and xe2x80x9ctagsxe2x80x9d are used interchangeably and refer to markers, labels, tags, and the like, used to trigger EAS systems.
Presently, many items of merchandise are source tagged. Source tagging is the attachment of EAS labels at the manufacturing or distribution site. Source tagging can result in an increase in a problem known as xe2x80x9ctag pollutionxe2x80x9d. Tag pollution refers to active or partially active labels inadvertently being carried into EAS equipped stores triggering the EAS alarm. When articles are source tagged with EAS labels, some of the tagged merchandise may be shipped to stores that are not equipped with EAS systems. With no EAS system in the store, when these tagged products are legitimately sold the EAS labels are not deactivated. The active EAS labels can trigger EAS alarms when the customer carries or wears an article, having an active label attached, into a store equipped with an EAS system.
Solutions to the tag pollution problem include providing security personnel at the store entrance to appropriately handle inadvertent EAS alarms. For example, EAS labels that alarm the system can be deactivated at the door. This solution can increase personnel costs and inconvenience to the customers. Alternately, the problem can be handled at the distribution point by properly deactivating EAS labels that are attached to products intended for stores without the appropriate EAS equipment. However, this can increase the time and costs associated with distribution. As more and more articles are source tagged with EAS labels, tag pollution will be an increasing problem.
U.S. Pat. No. 5,574,431 (the ""431 patent) discloses a security tag that is deactivatable as a result of stress induced by ordinary use of the article. The ""431 patent is directed to radio frequency (RF) tags, which work in RF EAS systems. RF EAS systems transmit and respond to RF energy in the interrogation zone. RF tags are comprised of a resonant circuit that detectably responds to the RF energy transmitted into the interrogation zone. The ""431 patent is directed to a mechanical stress concentrator that breaks the resonant circuit at a stress concentration point due to the stress caused by ordinary use of the article. The resonant circuit is opened and becomes disabled preventing the circuit from resonating when exposed to the interrogating RF energy. Thus, normal wearing of RF EAS tagged articles deactivates the attached RF EAS tags reducing the tag pollution problem.
Magnetomechanical EAS markers do not contain resonant circuits in an analogous manner to RF tags. A magnetomechanical EAS marker is made of an elongated strip of magnetostrictive ferromagnetic material, the xe2x80x9cresonatorxe2x80x9d, disposed adjacent a hard ferromagnetic element that, when magnetized, magnetically biases the strip and arms it to resonate mechanically at a preselected magnetic resonant frequency. The resonator is captured within a cavity in the marker housing so that it is free to mechanically vibrate. The hard ferromagnetic element, or bias, is a high coercivity biasing magnet that is capable of applying a DC magnetic bias field to the resonator. The bias magnet is positioned adjacent the resonator, but not in direct contact. The marker resonates when subjected to a magnetic interrogation field at a frequency at or near the marker""s resonant frequency. The response of the marker at the marker""s resonant frequency can be detected by EAS receiving equipment, thus providing an electronic marker for use in magnetomechanical EAS systems. Demagnetizing the bias magnet deactivates the marker. U.S. Pat. No. 4,510,489 discloses further information about magnetomechanical EAS systems.
U.S. Pat. No. 5,729,200, (the ""200 patent) the disclosure of which is incorporated herein by reference, discloses that conventional magnetomechanical EAS markers use amorphous metal alloys such as Metglas 2628CoA, having a composition of Fe32Co18Ni32B13Si5, and Metglas 2826MB, both available from Honeywell AlliedSignal, Inc. Parsippany, N.J., and VC4613 available from Vacuumschmelze GmbH, Grxc3xcner Weg 37, D-63450, Hanau, Germany, and other similar alloys for the active resonator. The bais magnet can be formed from a semi-hard magnetic material, such as SemiVac 90 available from Vacuumschmelze, Hanau, Germany, having a coercivity of around 70 to 80 Oersteds (Oe), and which requires an AC deactivation magnetic field of about 200 Oe. Alternately, a low coercivity material, such as SensorVac, also available from Vacuumschmelze, having a coercivity of about 20 Oe, can be used for the bias magnet, which requires a lower deactivation field that is useful for source tagged articles as described in the ""200 patent. A characteristic of all conventional bias magnet materials is that they are selected to have low magnetostriction so that stress induced by normal handling of the markers, and the articles to which the markers are attached, does not cause deactivation.
A method of deactivating a magnetomechanical EAS marker attached or contained within an article by stress induced by ordinary use of the article is needed.
A first aspect of the present invention is a deactivatable magnetomechanical electronic article surveillance marker with a magnetostrictive resonator adapted to mechanically resonate at a frequency within a preselected detection frequency range provided by an incident magnetic field. A magnetizable bias magnet is disposed adjacent the resonator that, when magnetized, biases the resonator with a magnetic field having a predetermined field strength to arm the resonator to resonate at the frequency. The bias magnet is magnetostrictive and demagnetizable by stress, such that normal use of an article incorporating the marker deactivates the marker. The marker can be incorporated into the article during manufacturing, or subsequent to manufacturing of the article.
The bias magnet can be made of an alloy composition containing a saturation magnetostriction of about 25 to about 50 parts per million (ppm). In one embodiment, the bias magnet is made of an alloy composition containing a saturation magnetostriction of about 50 ppm.
A second aspect of the present invention is a deactivatable magnetomechanical electronic article surveillance marker having a marker housing attachable to an article, a magnetostrictive resonator adapted to mechanically resonate at a frequency within a preselected detection frequency range provided by an incident magnetic field is disposed within the marker housing. A magnetizable bias magnet is disposed adjacent said resonator that, when magnetized, biases said resonator with a magnetic field having a predetermined field strength to arm the resonator to resonate at the frequency. A mechanism as described herein is disposed adjacent the marker housing for compressing the marker housing during ordinary usage of the article to dampen the mechanical resonance of the magnetostrictive resonator.
A mechanical deactivator can be attached to the marker housing and has a moveable member with a free end terminating in a pointed protrusion. The moveable member is adapted to move towards the marker housing forcing the pointed protrusion into the marker housing during ordinary usage of the article to dampen the resonance of the magnetostrictive resonator.
The bias magnet can be magnetostrictive and demagnetizable by stress, wherein normal use of the article incorporating the marker deactivates the marker, so that the marker includes both modes of deactivation.
Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention.